Silicon Carbide Thin Films and Vapor Deposition Methods Thereof

ABSTRACT

A vapor deposition process is provided for the growth of as-deposited hydrogen-free silicon carbide (SiC) and SiC films including oxygen (SiC:O) thin films. For producing the SiC thin films, the process includes providing a silahydrocarbon precursor, such as TSCH (1,3,5-trisilacyclohexane), in the vapor phase, with or without a diluent gas, to a reaction zone containing a heated substrate, such that adsorption and decomposition of the precursor occurs to form stoichiometric, hydrogen-free, silicon carbide (SiC) in a 1:1 atom ratio between silicon and carbon on the substrate surface without exposure to any other reactive chemical species or co-reactants. For the SiC:O films, an oxygen source is added to the reaction zone to dope the SiC films with oxygen. In the silahydrocarbon precursors, every carbon atom is bonded to two silicon atoms, with each silicon atom being additionally bonded to two or more hydrogen atoms.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 63/085,617, filed Sep. 30, 2020, the entire disclosure of which isherein incorporated by reference.

BACKGROUND OF THE INVENTION

Silicon carbide (SiC) thin films are witnessing an ever-increasingintensity of research interest across multiple application sectors. Theappeal of SiC coatings is attributed to their highly desirablecombination of physical, mechanical, electrical, and optoelectronicproperties, making them prime candidates for applications in theautomotive, aerospace, computer chip, solar, light-emitting, and medicalindustries.

SiC coatings are employed as hard protective coatings under challengingthermal, environmental, and chemical conditions due to their highhardness (potentially in excess of 40 GPa), effective oxidationresistance, elevated temperature and thermal shock resistance, as wellas chemical stability, and attractive mechanical, tribological anddielectric properties. Ultrathin SiC films are utilized in a broadspectrum of applications in integrated circuitry (IC) technologies,particularly in the microprocessor unit (MPU), system-on-a-chip (SoC),flash memory, and the vertical stacking of electronic devices in what iscommonly referred to as three-dimensional (3D) integrated systems. Forone, SiC is applied as a diffusion barrier in combination with lowdielectric constant (κ) material replacements to silicon dioxide (SiO₂).Similarly, SiC is used as a capping layer and an etch stop for copperinterconnects.

In an analogous manner, SiC thin films are successfully incorporatedinto active optical and optoelectronic devices due to their wide bandgap (2.3 eV) and elevated electrical breakdown voltage, including paneldisplays, lighting, and light-emitting devices. In this respect, SiCthin films are employed as permeation barriers and encapsulation layersin light-emitting devices (LEDs) and organic LEDs (OLEDs), as well as inthe fabrication of various planar optical systems and opticalwaveguides. Additionally, SiC coatings are suggested for use aspassivation layers in flexible electroluminescent devices. Theapplication of SiC also extends into the green energy field, primarilyin solar cell applications. For example, microcrystalline and amorphousSiC coatings are employed as window layers in thin film solar cells. Aswith the hard coatings and computer chip industries, SiC thin films areapplied as passivation layers in silicon solar cells.

Despite these extensive R&D efforts, significant challenges must beovercome to enable the extendibility of SiC thin films to emergingindustrial usages, such as heterodevice applications. For one, the lionshare of current SiC vapor phase deposition processes rely on the hightemperature reaction of silane- or halide-type precursors, such as SiH₄,Si₂H₆, and SiCl₄, with C-containing precursors, such as CHCl₃, C₃H₄,C₂H₂, and CCl₄. The inherent challenges associated with the use of suchchemistries are well documented and include their pyrophoric nature,numerous environmental, health, and safety issues, the incorporation ofhigh levels of hydrogen in the resulting SiC films, and the need forpost-deposition annealing to achieve the desired SiC filmspecifications. Two parameters for describing the quality ofhydrogenated amorphous silicon carbide thin films are addressed in theempirical formula a-Si_(1−x)C_(1+x):H where x is associated withsubstitutional bonding of hydrogen to the silicon atom, which prevents a1:1 stoichiometry of Si to C atoms, and the :H represents doped(including possibly interstitial) H atoms that do not change thestoichiometry of Si:C from 1:1. It is highly desirable for good qualitysilicon carbide to possess the minimum level of both types of H defects.

Prior art efforts to address these challenges include the use ofplasma-assisted atomic layer deposition (PA-ALD) of TSCH(1,3,5-trisilacyclohexane) at temperatures below 600° C., and preferablybetween 100 and 200° C. (U.S. Pat. No. 8,440,571); the application ofultra-violet light treatment to selectively remove some precursorligands and attachments to realize molecular layer deposition (U.S. Pat.No. 8,753,985); and remote plasma processes to form plasma effluentsthat generate a flowable layer on a substrate (U.S. Patent ApplicationPublication No. 2013/0217239). Unfortunately, all of these methodologiesfailed to deposit a true SiC phase which is stoichiometric and insteadyielded films consisting of networks of silicon-carbon-hydrogenarrangements, with different ratios of silicon to carbon, varyinghydrogen content, and significant defect levels. Not only is theinclusion of hydrogen a real concern due to its major impact on thephysical, chemical, electrical, and optoelectronic properties of thefilm, but the nature of the Si—H versus C—H bonding also plays a majorrole in tailoring the resulting film characteristics.

Another influencing factor is the Pauling relative electronegativity ofthe Si, C, and H elements (namely, Si:1.90; C:2.55; H:2.20). Si—C bondshave relatively high dipole moments, whereas Si—H bonds have relativelylow dipole moments. Thus, even if the atomic percentage of filmcompositions prepared using known methods are identical, the resultingfilms may have different atom bonding arrangements and the dielectricproperties of the resulting films may vary. Furthermore, the need forpost-deposition high temperature annealing to remove H and reduce thedensity of defects adds complexity and cost and limits the use of suchknown processes to applications that do not require thermally fragilesubstrates.

Other attempts at resolving these issues included a soft templatingapproach (STA) using TSCH with the final material being defined by theself-assembly of a soluble directing agent (SDA) into a solvent; the SDAacted as a supramolecular template and the solvent had the function ofSiC precursor. However, the process suffered from many challenges thatrendered it highly undesirable for semiconductor, optical, andoptoelectronic applications. These challenges include: (i) precursorpyrolysis is performed at very high temperature (1000° C.); (ii) the SDAmedium requires a week to achieve polymerization; (iii) the resultingSiC cannot be grown as a thin film but a powder exhibiting a porousgranular morphology as stacked spherical grains: and (iv) the STAprocess is a solvent based liquid phase which is not conducive forintegration into the prevailing manufacturing processes of thesemiconductor, energy, optical, and optoelectronic industries.

For these reasons, it would be desirable to provide a vapor depositiontechnique that overcomes the drawbacks of these and other knowndeposition techniques by forming high-quality, stoichiometric,as-deposited SiC thin films with minimal defect and hydrogen inclusion,while eliminating the issues associated with current silicon and carbonsource precursors. It would further be desirable if the vapor depositiontechnique minimizes the number and complexity of current processingconditions, thereby maximizing process safety, efficiency, andproductivity. It is also desirable if such a vapor deposition techniquecontrols the SiC microstructure by varying the processing parameters,such as substrate temperature and precursor flow rate, without the needfor a subsequent annealing step to achieve crystalline SiC.

BRIEF SUMMARY OF THE INVENTION

In one embodiment of the disclosure, a method for producing anas-deposited SiC thin film containing not more than 1 atomic % hydrogenonto a substrate in a reaction zone of a deposition chamber, comprises:

-   -   providing a substrate in a reaction zone of a deposition        chamber;    -   heating a substrate to a temperature of about 600° C. to about        1000° C.; and    -   providing a precursor comprising a silahydrocarbon, wherein        every carbon atom in the silahydrocarbon is bonded to two        silicon atoms, with each silicon atom being additionally bonded        to two or more hydrogen atoms, in the vapor phase without a        carrier gas to the reaction zone containing the substrate; and    -   wherein a layer of SiC is formed on a substrate surface by        adsorption and decomposition of the precursor;    -   wherein the adsorption and decomposition occur on the substrate        surface without the presence of any other reactive chemical        species or co-reactants.

In another embodiment, the disclosure provides a method for producing anas-deposited SiC thin film containing not more than 0.2 atomic %hydrogen onto a substrate in a reaction zone of a deposition chamber,the method comprising:

-   -   providing a substrate in a reaction zone of a deposition        chamber;    -   heating a substrate to a temperature of about 700° C. to about        1000° C.; and    -   providing a precursor comprising a silahydrocarbon, wherein        every carbon atom in the silahydrocarbon is bonded to two        silicon atoms, with each silicon atom being additionally bonded        to two or more hydrogen atoms, in the vapor phase without a        carrier gas to the reaction zone containing the substrate;    -   wherein a layer of SiC is formed on a substrate surface by        adsorption and decomposition of the precursor;    -   wherein the adsorption and decomposition occur on the substrate        surface without the presence of any other reactive chemical        species or co-reactants. In a further embodiment, the disclosure        provides a method for producing an as-deposited SiC:O thin film        containing not more than 1 atomic % hydrogen onto a substrate in        a reaction zone of a deposition chamber, the method comprising:    -   providing a substrate in a reaction zone of a deposition        chamber;    -   heating a substrate to a temperature of about 600° C. to about        1000° C.;    -   providing a precursor comprising a silahydrocarbon, wherein        every carbon atom in the silahydrocarbon is bonded to two        silicon atoms, with each silicon atom being additionally bonded        to two or more hydrogen atoms, in the vapor phase without a        carrier gas to the reaction zone containing the substrate; and    -   simultaneously providing a co-reactant reactive        oxygen-containing gas to the reaction zone containing the        substrate;    -   wherein a layer of SiC:O is formed on a substrate surface by        adsorption and decomposition of the precursor.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description of preferred embodiments of thepresent invention will be better understood when read in conjunctionwith the appended drawing. For the purposes of illustrating theinvention, there are shown in the drawings embodiments which arepresently preferred. It is understood, however, that the invention isnot limited to the precise arrangements and instrumentalities shown. Inthe drawings:

FIG. 1 is a representative XPS profile of Si and C concentrations versuspenetration depth in SiC for films deposited at 850° C. according to anembodiment of the disclosure showing an Si:C atomic ratio ranging from1:0.98 to 1:1.02 (nominally 1:1);

FIG. 2 is a representative high-resolution XPS spectrum for Si2p bindingenergy in SiC for films deposited at 850° C. according to an embodimentof the disclosure, corresponding to stoichiometric Si:C;

FIG. 3 is a graph of FTIR absorption coefficient versus wavenumber forSiC deposited at 850° C. and annealed at 1000° C. according to anembodiment of the disclosure;

FIG. 4 is a graph of FWHM at FTIR peak for SiC as a function ofdeposition temperature according to an embodiment of the disclosure;

FIG. 5 depicts the FTIR normalized absorbance coefficient foras-deposited SiC films using TSCH as Si precursor according to anembodiment of the disclosure versus post-annealed SiC films depositedusing a baseline (control) Si-source precursor;

FIG. 6 depicts photoluminescence (PL) measurements for as-deposited SiCfilms using TSCH as Si precursor according to an embodiment of thedisclosure versus SiC films deposited using a baseline (control)Si-source precursor;

FIG. 7 depicts FWHM and peak position of the SiC FTIR peak for an SiCmaterial according to an embodiment of the disclosure and a TMDSBcontrol as a function of substrate temperature;

FIG. 8 is a graph of growth rate as a function of deposition temperaturefor SiC films at 0.2 Torr according to embodiments of the disclosure;

FIG. 9 plots the refractive index (n) and absorption coefficient (a)values for SiC films at 500 nm wavelength as determined by ellipsometryversus substrate temperature according to embodiments of the disclosure;

FIG. 10 is a graph of the absorption coefficients for SiC grown at 650°C. from TSCH versus a control (TMDSB) SiC sample according to anembodiment of the disclosure;

FIG. 11 (a) are FTIR spectra for SiC samples deposited at threedifferent deposition temperatures (650° C., 700° C., and 800° C.)according to embodiments of the disclosure for the expanded wavenumberrange from 500 to 3000 cm⁻¹; and

FIG. 11 (b) is an enlarged version of the absorption peak around 2090cm⁻¹ from FIG. 11(a) corresponding to the Si—H stretching mode to give abetter perspective of the size of the Si—H peak.

DETAILED DESCRIPTION OF THE INVENTION

The disclosure relates to vapor deposition processes for producingas-deposited crystalline and amorphous silicon carbide (SiC) thin filmsand SiC films including oxygen (SiC:O thin films) having extremely lowconcentrations of structural and compositional defects, in particulardefects associated with variations from the ideal stoichiometry ofsilicon carbide (Si:C=1:1) and substitutional and interstitial defectsassociated with the presence of hydrogen, as well as to the filmsproduced from such processes. It is generally considered in the art thatthin silicon carbide films with levels of 10 atomic % hydrogen or lessare considered to exhibit “low levels of hydrogen incorporation” andthat films having hydrogen levels of 1 atomic % or less are consideredto be “hydrogen free” (see, for example, A. Kleinováet al, “FTIRspectroscopy of silicon carbide thin films prepared by PECVD technologyfor solar cell application,” Proc. SPIE 9563, Reliability ofPhotovoltaic Cells, Modules, Components, and Systems VIII, 95630U(September 2015); S. Gallis et al “Photoluminescence at 1540 nm fromerbium-doped amorphous silicon carbide films” J. Mater. Res., 19(8),2389-2893, 2004).

The processes described herein may be used to produce both SiC filmswith low levels of hydrogen incorporation and hydrogen-free SiC films,as defined above, as well as SiC:O thin films. Consistent with thecurrent terms of art, a film containing “a low level of hydrogen” meansthat the film contains 10 atomic % hydrogen or less, “hydrogen-free”means that the film contains 1 atomic % or less hydrogen, and a filmwith “non-detectable” hydrogen contains 0.2 atomic % or less hydrogen.For the purposes of this disclosure, silicon carbide films withnon-detectable hydrogen may also be understood to refer to films havinghydrogen contents below the detection limits of spectroscopy methods andapparatuses, such as infrared spectroscopy (IR) and X-ray photoelectronspectroscopy (XPS), which is estimated to be at or below 0.2 atomic %.

The term “thin film” is well understood in the art, and may includefilms ranging in thickness from a few nanometers to a few microns. Morespecifically, the term “thin film” may be understood to refer to a filmhaving a thickness of less than 500 nm and preferably between 2 and 50nm. The phrase “as-deposited” would be understood in the art to meanthat the film has the properties of utility immediately after depositionwithout further treatment such as plasma processes, irradiation, orthermal annealing.

For producing SiC thin films, the processes according to the disclosureinvolve providing a silahydrocarbon precursor as described below, suchas the preferred TSCH (1,3,5-trisilacyclohexane), in the vapor phase,with or without a carrier or diluent gas, to a reaction zone containinga heated substrate, such that adsorption and decomposition of theprecursor occurs to form stoichiometric silicon carbide (SiC) in a Si:Catomic ratio ranging from 1:0.98 to 1:1.02, nominally 1:1, on thesubstrate surface without additional exposure to any other reactivechemical species or co-reactants. For forming SiC:O films, an oxygensource is added to the reaction zone to modulate doping. Alternatively,the as-deposited SiC films may be subsequently reacted or treated withan oxygen source. The grain size and morphology of the SiC and SiC:Ofilms can be modulated by controlling the processing parameters, such assubstrate temperature and precursor flow rate, without the need for asubsequent annealing step to achieve crystalline films. However,annealing may also be implemented if larger crystalline grains orepitaxial phase are desirable.

The vapor deposition techniques described herein overcome the drawbacksof known deposition techniques and enable the growth of high-quality,stoichiometric, as-deposited SiC thin films with 1% or less defectsand/or hydrogen without the need for post deposition annealing, whileeliminating the issues associated with current Si and C sourceprecursors and minimizing the number and complexity of presentprocessing conditions, thereby maximizing process safety, efficiency,and productivity.

The resulting SiC thin films would be highly advantageous for criticalapplications in the semiconductor, energy, optical, and optoelectronicindustries. In particular, the presence of extremely low levels ofdefects and hydrogen in the as-deposited SiC thin films make them idealfor incorporation in optical and photoluminescent devices in which theinclusion of defects and hydrogen in as-deposited SiC tend to hinderoptical and photoluminescent performance and require high-temperatureannealing to remedy such deficiencies. In contrast, the presence ofextremely low levels of defects and hydrogen in as-deposited SiC filmsas described herein enables the micromodulation of the concentration andoptical performance of dopants, such as oxygen and erbium, and maximizesoptical and photoluminescent performance in the resulting devices andsystems.

The processes according to the disclosure employ a class of silicon- andcarbon-containing source precursors, carbosilanes, alternately denotedsilahydrocarbons, in which every carbon atom in the silahydrocarbon isbonded to two silicon atoms, with each silicon atom being additionallybonded to two or more hydrogen atoms. The ratio of silicon atoms tocarbon atoms in the precursor is preferably in the range of about 1 to1.5. Exemplary precursors include 1,3,5,7-tetrasilanonane;1,3,5,7-tetrasilacyclooctane; tricyclo[3.3.1.13,7]pentasilane; and1,3-disilacyclobutane (which are not readily available), and preferredcommercially available precursors include 1,3,5-trisilapentane and1,3,5-trisilacyclohexane (TSCH); the most preferred is the commerciallyavailable cyclic carbosilane 1,3,5-trisilacyclohexane (TSCH). Unlikesilane- or halide-type silicon precursors such as SiH₄, Si₂H₆, andSiCl₄, this class of Si precursors contains both silicon and carbonatoms, thus providing a decomposition pathway for the formation ofstoichiometric SiC without the need for a carbon-containing co-reactant.The chemical structure and bonding configuration of thesilahydrocarbon-type precursors such as TSCH enable decomposition whichyields stoichiometric SiC at lower temperatures than are required in thereaction of silane- or halide-type precursors, such as SiH₄, Si₂H₆, andSiCl₄, with carbon-containing precursors, such as CHCl₃, C₃H₄, C₂H₂, andCCl₄, and without the need for a post-deposition annealing step.

Appropriate substrates include the preferred silicon, as well as, forexample and without limitation, silicon oxide, silicon nitride, siliconcarbide, gallium nitride, cobalt, ruthenium, copper, platinum, titanium,titanium nitride, tantalum, tantalum nitride, substrates that are usedin optical and photoluminescence applications, among others.

An important aspect of the vapor deposition techniques described hereinis that the processes are based on tightly controlled experimentalconditions including source precursor temperature, substratetemperature, precursor flow rate, precursor partial pressure in thereaction zone, and total process pressure to ensure that the sourceprecursor decomposition pathways occur in the surface-reaction-limitedregime and not the mass-transport-limited regime. These parametersensure tight control of the adsorption and decomposition mechanisms ofthe silahydrocarbon-type precursors to optimize the energetics of ligandremoval and hydrogen-elimination, while maintaining the integrity ofSi—C bonds to yield a 1:1 Si:C ratio in the resulting films.

In this surface-reaction-limited regime, and while not wishing to bebound by theory, the methods described herein ensure that two criticalprocesses are occurring: (i) an elimination reaction in which a Si—Cdouble bond structure “silene,” is formed, followed by (ii) adissociative adsorption of hydrogen from the silicon atoms, which,depending on deposition parameters, particularly substrate temperature,produces SiC films that can be described as films with low hydrogencontent<10 atom % hydrogen), hydrogen-free (less than 1 atom % hydrogen)or having no detectable hydrogen content (<0.2% atom % hydrogen).Further, the resulting SiC films consist only of simple cross-linkedSi—C bonds with less than 0.2% variation from 1:1 Si:C stoichiometry(which can be expressed as a range of 1:0.98 to 1:1.02), regardless ofsubstrate deposition temperature. These films are in stark contrast toprior art films in which the SiC matrix exhibits a transition frompredominantly C—Si to C—C, C—Si, and C—H type bonds, while siliconevolved from Si—C bonds to Si—C, Si—Si, and Si—H bonds as function ofprocessing conditions, resulting in various temperature-dependentcomplex bonding configurations in SiC films with the inclusion of a highdefect density and significant hydrogen content.

“Low hydrogen content” may also be understood to refer to a material inwhich a ratio of the integrated area under the Si—H bond peak at ˜2080cm⁻¹ to the integrated area under the Si—C bond peak at ˜730 cm⁻¹ asmeasured by infrared spectroscopy is less than 1:50 using standardspectroscopy techniques. “Low hydrogen content” may further beunderstood to refer to a material in which a ratio of the Si—H bonddensity to the Si—C bond density of less than 1:50 ratio as measured byinfrared spectroscopy. It should be noted that the ratio of these IRabsorption peaks is simply a correlation demonstrating extremely lowlevels of Si—H bonds below the detection limits of IR. Alternatively, alow level of hydrogen incorporation (as well as other defects asdescribed above) could be determined by observing an undoped SiCabsorption coefficient below 10³ cm⁻¹ in the visible optical band whenexcited @ 1.75 eV using spectroscopic ellipsometry.

In a preferred embodiment, films having 1:1 Si:C stoichiometry and nodetectable hydrogen (less than 0.2 atomic %) can be prepared atsubstrate deposition temperatures greater than about 700° C. and lessthan about 1000° C. In other embodiments, in which higher contents ofhydrogen are acceptable but 1:1 Si:C stoichiometry is still arequirement, process temperatures are in the range of between about 600°C. and about 700° C., which has benefits both in terms of less exposureof devices to thermal damage and energy efficiency. For example, atdeposition temperatures of 650° C., hydrogen content of the films isdetectable at levels estimated at 0.2-1.0 atomic % while filmstoichiometry is maintained. It is noted that the above ranges areintended to include all temperatures within these ranges such as, butnot limited to, 600° C., 625° C., 650° C., 675° C., 700° C., 725° C.,750° C., 775° C., 800° C., 825° C., 850° C., 875° C., 900° C., 925° C.,950° C., 975° C., and 1000° C. Preferred substrate depositiontemperatures are about 700° C. to about 850° C., such as 700° C., 725°C., 750° C., 775° C., 800° C., 825° C., and 850° C.

In one embodiment, aspects of the disclosure relate to a method forproducing as-deposited, hydrogen-free (not more than 1 atomic %hydrogen), crystalline SiC thin films which involves providing asilahydrocarbon-type precursor as described above, such as the preferredTSCH, in the vapor phase, without a carrier gas, to a reaction zone of adeposition chamber containing a heated substrate as described above at atemperature of about 600° C. to about 1000° C. (preferably about 700° C.to about 1000° C.), such that adsorption and decomposition of the TSCHor other precursor occurs on the substrate surface to form a layer ofSiC on the substrate without the presence of any other reactive chemicalspecies or co-reactants. The decomposition process yields as-deposited,hydrogen-free, crystalline SiC films, without the need for apost-deposition annealing step. It is also within the scope of thedisclosure to provide the precursor in the vapor phase with a diluentinert non-reactive gas, as this may offer practical advantages orconvenience, but the diluent gas is not required.

The source temperature of the TSCH or other precursor is maintained atabout −25 to about 75° C., more preferably at about 0 to about 25° C.,and the partial vapor pressure of the precursor in the depositionchamber is maintained at about 10% to about 100% of the total pressurein the reaction zone, more preferably at about 50% to about 90% of thetotal pressure in the reaction zone; the remaining partial pressure isfrom the diluent gas, if present. If there is no diluent gas, the vaporpressure of the precursor is the total pressure of the system, and nodiluent or carrier gas is needed since the precursor vapor pressurealone sustains the total pressure (vacuum) in the system. The substratedeposition temperature is maintained at about 600° C. to about 1000° C.,and more preferably at about 700 to about 850° C. The total pressure inthe reaction zone (deposition chamber), also referred to as workingpressure, is maintained at about 0.1 torr to about 760 torr, and morepreferably 0.2 torr to 10 torr. Also, the diluent gas flow rate (ifemployed) is maintained at from about 10 to about 1000 sccm, and morepreferably 50 to 250 sccm.

The diluent gas, if employed, is selected from known inert gases such ashelium, neon, argon, and xenon.

Employing these process parameters to form an SiC film ensures a Si:Cstoichiometry of 1:1±0.05, preferably 1:1±0.02 (1:1.098 to 1:1.02) asmeasured by XPS and with less than 1 atomic percent hydrogen as measuredby infrared spectroscopy. Further, a ratio of the integrated area underthe Si—H bond peak at ˜2080 cm-1 for the SiC film as measured byinfrared spectroscopy to the integrated area under the Si—C bond peak at˜730 cm-1 as measured by infrared spectroscopy is less than about 1:50.

In another embodiment, aspects of the disclosure relate to a method forproducing as-deposited, crystalline SiC films with non-detectableconcentrations (not more than 0.2 atomic %) of H (both interstitial andsubstitutional) and defects. The method involves providing TSCH oranother silahydrocarbon-type precursor as described above in the vaporphase to a reaction zone of a deposition chamber containing a heatedsubstrate as described above at a temperature of about 700° C. to about1000° C. (preferably about 700° C. to about 850° C.), such thatadsorption and decomposition of TSCH or other precursor occurs on thesubstrate surface in the presence of the diluent inert non-reactive gasto form a layer of SiC on the substrate and without the intervention ofany other reactive chemical species or co-reactants. The decompositionprocess yields as-deposited, crystalline SiC films, with non-detectableH (both interstitial and substitutional) and defects as described abovewithout the need for a post-deposition annealing step. It is also withinthe scope of the disclosure to provide the precursor in the vapor phasewith a diluent inert non-reactive gas, as this may offer practicaladvantages or convenience, but the diluent gas is not required.

The source temperature of the TSCH or other precursor is maintained atabout −25 to about 75° C., more preferably at about 0 to about 25° C.,and the partial vapor pressure of the precursor in the depositionchamber is maintained at about 10% to about 100% of the total pressurein the reaction zone, more preferably at about 50% to about 90% of thetotal pressure in the reaction zone; the remaining partial pressure isfrom the diluent gas, if present. If there is no diluent gas, the vaporpressure of the precursor is the total pressure of the system, and nodiluent or carrier gas is needed since the precursor vapor pressurealone sustains the total pressure (vacuum) in the system. The substratedeposition temperature is maintained at about 700° C. to about 1000° C.,and more preferably at about 700 to about 850° C. The total pressure inthe reaction zone (deposition chamber), also referred to as workingpressure, is maintained at about 0.1 torr to about 760 torr, and morepreferably 0.2 torr to 10 torr. Also, the diluent gas flow rate (ifemployed) is maintained at from about 10 to about 1000 sccm, and morepreferably 50 to 250 sccm.

The diluent gas, if employed, is selected from known inert gases such ashelium, neon, argon, and xenon.

Employing these process parameters to form an SiC film ensures a Si:Cstoichiometry of 1:1±0.05, preferably 1:1±0.02 (1:1.098 to 1:1.02) andwith less than 1 atomic percent hydrogen. Further, a ratio of theintegrated area under the Si—H bond peak at ˜2080 cm-1 for the SiC filmas measured by infrared spectroscopy to the integrated area under theSi—C bond peak at ˜730 cm-1 as measured by infrared spectroscopy is lessthan about 1:50.

In a further embodiment, aspects of the disclosure relate to a methodfor producing as-deposited, SiC:O films containing not more than 1atomic % hydrogen. The method involves providing TSCH (or otherprecursor as defined above) in the vapor phase, without a carrier ordiluent gas, to a reaction zone of a deposition chamber containing aheated substrate at a temperature of about 600° C. to about 1000° C.(preferably about 700° C. to about 850° C.), as described above, andsimultaneously introducing an oxygen-containing gas to the reaction zoneof the deposition chamber, such that adsorption and decomposition ofTSCH occurs on the substrate surface with the presence of the reactiveoxygen-containing gas as a co-reactant to form a layer of SiC:O on thesubstrate surface. It is also within the scope of the disclosure toprovide the precursor in the vapor phase with a diluent inertnon-reactive gas, as this may offer practical advantages or convenience,but the diluent gas is not required. The decomposition process yieldsas-deposited, hydrogen-free SiC:O films, i.e., films containing not morethan 1 atomic % hydrogen.

The source temperature of the TSCH or other precursor is maintained atabout −25 to about 75° C., and more preferably about 0 to about 25° C.,and the TSCH partial vapor pressure in the deposition chamber ismaintained at about 10% to about 100% of the total pressure in thereaction zone, and more preferably at about 50% to about 90% of thetotal pressure in the reaction zone. The oxygen-containing gasco-reactant flow rates are set to achieve a corresponding partial vaporpressure in the reaction zone of about 1% to about 25% of that of thecarbosilane precursor, and more preferably about 5% to about 10% of thecarbosilane precursor. The substrate deposition temperature ismaintained at about 600° C. to about 1000° C., and more preferably about700 to about 850° C. The total pressure in the reaction zone (depositionchamber), also referred to as working pressure, is maintained at about0.1 torr to about 760 torr, and more preferably 0.2 torr to 10 torr.Also, the diluent gas flow rate (if employed) is maintained at fromabout 10 to about 1000 sccm, and more preferably 50 to 250 sccm.

The diluent gas, if employed, is selected from known inert gases such ashelium, neon, argon, and xenon. The oxygen-containing gas co-reactant isselected from a group consisting of oxygen, water, ozone, nitrous oxide,and other typical oxygen containing reactants which are known in theart.

Alternatively, the as-deposited SiC films may be subsequently treatedin-situ (prior to removal from the deposition chamber) or ex-situ (byremoving them from the deposition chamber and placing them in a furnaceor annealing chamber) by exposure to an oxygen-containing source to formSiC:O films.

It is also within the scope of the disclosure to replace some or all ofthe hydrogen atoms which are bonded to the silicon atoms in theprecursors with deuterium atoms. This offers the advantage ofeliminating substitutional defects associated with Si—H bond infraredabsorption in the range of 2000-2260 cm-¹ and even further reduces theoverall concentration of interstitial defects (if they exist) sincedeuterium has less tendency than hydrogen to cause the dislocationsassociated with hydrogen in amorphous silicon and silicon carbidesystems. In the case of trisilacyclohexane, all six of the hydrogenatoms are replaced with deuterium atoms. This compound is readilyproduced by utilizing lithium aluminum deuteride to reduce ahexaalkoxyltrisilacyclohexane intermediate. As another example, theeight hydrogen atoms bonded to silicon in trisilapentane can be replacedwith deuterium in a similar fashion.

The invention will now be described in connection with the following,non-limiting examples. These examples describe the deposition ofstoichiometric SiC films from TSCH (1,3,5-trisilacyclohexane) on Sisubstrates with extremely low levels of defects and hydrogen.

Example 1: Identification of Optimized Process Window

Six stoichiometric SiC films were produced by the decomposition of TSCH(1,3,5-trisilacyclohexane) on Si substrates using the processingparameters summarized in Table I.

TABLE I Processing parameters for producing SiC from TSCH as sourceprecursor Precursor Dilution Gas Precursor Partial Source PrecursorSubstrate Pressure (Ar) Pressure in Film Temperature Flow RateTemperature (Vacuum) Flow Rate reaction zone Thickness Run (° C.) (sccm)(° C.) (torr) (sccm) (torr) (nm) 1 50° C. 1 800 0.50 200 0.40 65 2 50°C. 1 850 0.50 200 0.40 89 3 50° C. 1 850 0.50 200 0.40 32 4 50° C. 1 8250.50 200 0.40 36 5 50° C. 1 800 0.50 200 0.40 37 6 50° C. 1 850 0.50 1000.45 120

The resulting films were analyzed by x-ray photoelectron spectroscopy(XPS), Fourier-transform infrared spectroscopy (FTIR), andphotoluminescence (PL) measurements.

Si and C concentrations versus penetration depth in the SiC films wereassessed by XPS depth profile analyses, as shown in FIGS. 1 and 2 foras-deposited SiC films grown at substrate temperatures of 850° C.Similar data were obtained for runs 2, 3, and 6 above, demonstrating therobustness of the deposition process. The data demonstrate a consistent1:1 Si:C atomic ratio throughout the films with an accuracy of 1:0.98 to1:1.02, demonstrating that the films are stoichiometric. Thehigh-resolution XPS spectrum for Si2p binding energies is displayed inFIG. 8 for SiC films deposited at 800° C.; both runs 1 and 5 (differentfilm thicknesses) gave the same XPS spectra. The Si2p binding energylocation at 100.3 eV confirms that the chemical bonding corresponds toSi—C(standard use: 3C—SiC).

FTIR analysis shows the following: (i) As shown in FIG. 3, a singlestrong absorption peak is observed around 800 cm⁻¹, corresponding toSi—C stretching mode in crystalline SiC. The FWHM of the FTIR peakdecreases from 62.0 to 49.8 cm⁻¹ after annealing at 1000° C. for 1 hour,indicating an increase in crystallinity due to annealing. (ii) As shownin FIG. 4, the FWHM of the FTIR peak decreases with increasingdeposition temperature, suggesting increased deposited crystallinitywith the rise in deposition temperature.

Example 2: Investigation of Process Parameters and Precursor Chemistry

Ten inventive stoichiometric SiC films were produced by thedecomposition of TSCH (1,3,5-trisilacyclohexane) on Si substrates, andtwo comparative SiC films (Runs 7 and 14) were produced as a control bythe decomposition of TMDSB (1,1,3,3-tetramethyl-1,3-disilacyclobutane)as a precursor on Si substrates. The processing parameters aresummarized in Table II below.

TABLE II Processing parameters for producing inventive and comparativeSiC films Precursor Dilution Gas Precursor Partial Source PrecursorSubstrate Pressure (Ar) Pressure in Temperature Flow Rate Temperature(Vacuum) Flow Rate reaction zone Run (° C.) Precursor (sccm) (° C.)(torr) (sccm) (torr) 7 50° C. TMDSB as 10 800 1 400 0.40 control orbaseline 8 50° C. TSCH 1 400 1 200 0.40 9 50° C. TSCH 1 450 1 200 0.4010 50° C. TSCH 1 500 1 200 0.40 11 50° C. TSCH 1 550 1 200 0.40 12 50°C. TSCH 1 600 0.2 200 0.15 13 50° C. TSCH 1 650 0.2 200 0.15 14 50° C.TMDSB as 10 800 1.5 400 0.15 control or baseline 15 50° C. TSCH 1 7000.2 200 0.15 16 50° C. TSCH 1 750 0.2 200 0.15 17 50° C. TSCH 1 800 0.2200 0.15 18 50° C. TSCH 1 850 0.2 200 0.15*(1,1,3,3-tetramethyl-1,3-disilacyclobutane)

FIG. 5 displays a comparison of the degree of crystallinity betweenpost-annealed SiC films deposited using the baseline source precursor asa control and as-deposited SiC films using TSCH as the precursor. TheFTIR spectra show that the as-deposited SiC films using the TSCHprecursor exhibit the same 100% crystallinity as the SiC films depositedfrom the baseline Si-source precursor after annealing at 1100° C. It isnoted that no deposition occurred for the baseline precursor TMDSB below800° C. and the as-deposited SiC from the comparative materialsincorporated high levels of H (more than 11 at %) and defects.

Photoluminescence (PL) measurements are shown in FIG. 6 for SiC filmsdeposited using the baseline TMDSB control precursor and SiC films usingTSCH as the precursor. It may be seen that the SiC films using TSCH as aprecursor exhibit negligible to no PL intensity, indicating asignificantly reduced defect density in comparison with the SiC filmsdeposited using the baseline (TMDSB) Si-source precursor.

FIG. 7 is a graph of FWHM and peak position of the SiC FTIR peak for theTMDSB control and TSCH inventive samples as s function of substratetemperature. The smaller FWHM and red-shifted peak position with therise in substrate temperature indicates higher crystallinity at higherdeposition temperature.

Also, the growth rate as a function of deposition temperature at 0.2Torr is shown in FIG. 8. The highest growth rate, observed at 850° C.,was 2.23 nm/s. As expected, the growth rate decreases with lowersubstrate temperature due to the reduction in the thermal energyavailable to the precursor decomposition reaction.

Representative atomic force microscopy (AFM) micrographs of the SiCsamples as a function of substrate temperature were measured (notshown). The root-mean-square (rms) surface roughness increased withhigher substrate temperature. This result is expected and is attributedto the increased crystallinity with higher substrate temperature.

Scanning electron microscope (SEM) results (not shown) for substratetemperatures of 800° C., 700° C., and 650° C., showed good correlationwith the AFM data in terms of rms surface roughness, which increasedwith higher substrate temperature.

The refractive index (n) and absorption coefficient (a) values for theSiC films at 500 nm wavelength as determined by ellipsometry are plottedversus deposition temperature in FIG. 9; n values are represented bycircles and a values are represented by triangles. The refractive indexn varied between 2.9 and 2.7 for all deposition temperatures, which isconsistent with the reference value for 3C—SiC (2.7), indicating astoichiometric SiC phase.

Furthermore, a comparison of absorption coefficient for SiC grown at650° C. from TSCH versus the control TMDSB SiC sample is shown in FIG.10. The TSCH SiC film shows a drastic decrease in absorption in thevisible range, in stark contrast with the control SiC sample whichexhibits high absorption throughout that energy range. This clearlydemonstrates a significantly lower defect density for SiC grown at 650°C. from TSCH versus the control SiC sample.

Finally, FIG. 11 (a) depicts the FTIR spectra for inventive SiC samplesdeposited at 3 different temperatures (650° C., 700° C., and 800° C.)for the expanded wavenumber range from 500 to 3000 cm⁻¹. The FTIRspectra show the following: (i) a single highly intense absorption peakaround 800 cm⁻¹ corresponding to Si—C stretching mode in crystallineSiC; and (ii) and an extremely small absorption peak around 2090 cm⁻¹corresponding to Si—H stretching mode for the sample grown at 650° C.The Si—H peak is reduced to below background signal for the samplesdeposited at 700° C. and 800° C., indicating that H in the SiC samplesis below the detection limits of FTIR. FIG. 11(b) is an enlarged versionof the absorption peak around 2090 cm⁻¹ corresponding to Si—H stretchingmode to give a better perspective of the size of the Si—H peak.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

We claim:
 1. A method for producing an as-deposited SiC thin filmcontaining not more than 1 atomic % hydrogen onto a substrate in areaction zone of a deposition chamber, the method comprising: providinga substrate in a reaction zone of a deposition chamber; heating asubstrate to a temperature of about 600° C. to about 1000° C.; andproviding a precursor comprising a silahydrocarbon, wherein every carbonatom is bonded to two silicon atoms, with each silicon atom beingadditionally bonded to two or more hydrogen atoms, in the vapor phasewithout a carrier gas to the reaction zone containing the substrate; andwherein a layer of SiC is formed on a substrate surface by adsorptionand decomposition of the precursor; wherein the adsorption anddecomposition occur on the substrate surface without the presence of anyother reactive chemical species or co-reactants.
 2. The method accordingto claim 1, wherein the substrate comprises silicon, silicon oxide,silicon nitride, silicon carbide, gallium nitride, cobalt, ruthenium,copper, platinum, titanium, titanium nitride, tantalum, or tantalumnitride.
 3. The method according to claim 1, wherein the precursorcomprises 1,3,5-trisilapentane; 1,3,5,7-tetrasilanonane;tricyclo[3.3.1.13,7]pentasilane; 1,3-disilacyclobutane;1,3,5-trisilacyclohexane (TSCH); or 1,3,5,7-tetrasilacyclooctane.
 4. Themethod according to claim 3, wherein the precursor comprises1,3,5-trisilacyclohexane (TSCH) or 1,3,5,7-tetrasilacyclooctane.
 5. Themethod according to claim 1, wherein the SiC thin film has a Si:C atomicratio of about 1:0.98 to 1:1.02.
 6. The method according to claim 1,wherein a ratio of the integrated area under the Si—H bond peak at ˜2080cm⁻¹ for the SiC film as measured by infrared spectroscopy to theintegrated area under the Si—C bond peak at ˜730 cm⁻¹ as measured byinfrared spectroscopy is less than about 1:50.
 7. The method accordingto claim 1, wherein the substrate is heated to a temperature of about700° C. to about 850° C.
 8. A method for producing an as-deposited SiCthin film containing not more than 0.2 atomic % hydrogen onto asubstrate in a reaction zone of a deposition chamber, the methodcomprising: providing a substrate in a reaction zone of a depositionchamber; heating a substrate to a temperature of about 700° C. to about1000° C.; and providing a precursor comprising a silahydrocarbon,wherein every carbon atom is bonded to two silicon atoms, with eachsilicon atom being additionally bonded to two or more hydrogen atoms, inthe vapor phase without a carrier gas to the reaction zone containingthe substrate; wherein a layer of SiC is formed on a substrate surfaceby adsorption and decomposition of the precursor; wherein the adsorptionand decomposition occur on the substrate surface without the presence ofany other reactive chemical species or co-reactants.
 9. The methodaccording to claim 8, wherein the substrate comprises silicon, siliconoxide, silicon nitride, silicon carbide, gallium nitride, cobalt,ruthenium, copper, platinum, titanium, titanium nitride, tantalum, ortantalum nitride.
 10. The method according to claim 8, wherein theprecursor comprises 1,3,5-trisilapentane; 1,3,5,7-tetrasilanonane;tricyclo[3.3.1.13,7]pentasilane; 1,3-disilacyclobutane;1,3,5-trisilacyclohexane (TSCH); or 1,3,5,7-tetrasilacyclooctane. 11.The method according to claim 10, wherein the precursor comprises1,3,5-trisilacyclohexane (TSCH) or 1,3,5,7-tetrasilacyclooctane.
 12. Themethod according to claim 8, wherein the SiC thin film has a Si:C atomicratio of about 1:0.98 to 1:1.02.
 13. The method according to claim 8,wherein a ratio of the integrated area under the Si—H bond peak at ˜2080cm⁻¹ for the SiC film as measured by infrared spectroscopy to theintegrated area under the Si—C bond peak at ˜730 cm⁻¹ as measured byinfrared spectroscopy is less than about 1:50.
 14. The method accordingto claim 8, wherein the substrate is heated to a temperature of about700° C. to about 850° C.
 15. A method for producing an as-depositedSiC:O thin film containing not more than 1 atomic % hydrogen onto asubstrate in a reaction zone of a deposition chamber, the methodcomprising: providing a substrate in a reaction zone of a depositionchamber; heating a substrate to a temperature of about 600° C. to about1000° C.; providing a precursor comprising a silahydrocarbon, whereinevery carbon atom is bonded to two silicon atoms, with each silicon atombeing additionally bonded to two or more hydrogen atoms, in the vaporphase without a carrier gas to the reaction zone containing thesubstrate; and simultaneously providing a co-reactant reactiveoxygen-containing gas to the reaction zone containing the substrate;wherein a layer of SiC:O is formed on a substrate surface by adsorptionand decomposition of the precursor.
 16. The method according to claim15, wherein the substrate comprises silicon, silicon oxide, siliconnitride, silicon carbide, gallium nitride, cobalt, ruthenium, copper,platinum, titanium, titanium nitride, tantalum, or tantalum nitride. 17.The method according to claim 15, wherein the precursor comprises1,3,5-trisilapentane; 1,3,5,7-tetrasilanonane;tricyclo[3.3.1.13,7]pentasilane; 1,3-disilacyclobutane;1,3,5-trisilacyclohexane (TSCH); or 1,3,5,7-tetrasilacyclooctane. 18.The method according to claim 17, wherein the precursor comprises1,3,5-trisilacyclohexane (TSCH) or 1,3,5,7-tetrasilacyclooctane.
 19. Themethod according to claim 15, wherein the substrate is heated to atemperature of about 700° C. to about 850° C.
 20. The method accordingto claim 15, wherein the oxygen-containing gas comprises oxygen, water,ozone, and/or nitrous oxide.